Java Networking II

1. Java Networking II IS 313 5.22.2003

2. Outline • Socket review • URL classes • Server programming example • Homework #4

3. Outline • Homework #3 solution • Homework #4 • Socket review • HTTP Protocol • URL and URLConnection • Example

4. Sockets Review • For applications to communicate, they need • a transport mechanism • an addressing mechanism • way to interact with these mechanisms • For client/server applications • client = caller, originates requests • server = listener, handles requests

5. Sockets Review II • Transport mechanism • TCP/IP • bi-directional data stream • Addressing mechanism • hostname • port number

6. Sockets Review III • Java classes • Socket for client • ServerSocket for server • But • a call to accept returns with a regular Socket when a client connects

7. Socket Review IV • Multi-threading • Extremely important for server applications • One thread listens continuously for connections • Other threads handle requests

8. Server Programming Example • WeatherServer • Protocol • one line commands: ADD and INFO • one line responses

9. Homework #4 • Networked version of FFGUIMode • In other words • turn FFGUIMode into a server • client already exists

10. Objectives • Add server thread to FFGUIMode to listen for connections • Add worker threads to execute commands • Add a Server menu to interface • Synchronize database access

11. New Package Structure • core • Command, CommandMap and basic commands • cmd • command implementations • db • database • ui • user interface • client • a text mode client • server • to be added

12. Client • TextModeClient • Looks like old FFTextMode • but • instead of creating and executing command objects • it sends messages to a server • What should those messages look like?

13. Homework #4 Protocol • Request #1 • prompts • command: name • Response #1 • OK • Enter first name: • Enter last name: • Request #2 • parameters • command: name • Response #2 • OK • first • last • Request #3 • name • first: Marilyn • last: Monroe • Response #3 • OK • Members with name: Marilyn Monroe • 54045 Monroe Marilyn 01/01/2003 75500 3 • Request #4 • parameters • command: nmae • Response #4 • ERROR • Unknown command: nmae

14. Stateless Protocol • Each request is a single connection • Worker thread • handles a single request • then terminates • Simplifies implementation

15. Alternatives • Session • login • make text mode requests • logout • worker handles whole interaction • Multi-request • transmit name of command • subsequent requests relative to command • worker handles whole command

16. Example • Program as it should run • Using telnet to test

17. URL classes

18. HTTP Protocol • Request • “I want something” • Response • “Here it is” • or “Not found” • Headers • Body

19. HTTP Response Example

20. Stateless • HTTP is stateless • Each request is treated independently of others • Problems • authorization • identity • “sessions”

21. URL • Example • http://www.cti.depaul.edu/people/ • Parts • Protocol • Host • Port • Path

22. In Java • URL classes • new URL (http://www.cti.depaul.edu/”) • Simplest case • url.getInputStream() • read from downloaded document

23. URLConnection • url.getConnection() • with URLConnection • initially “unconnected” state • can modify request properties/headers • connect() or getInputStream() • “connected” state • can read response properties/headers

24. Example